Fluid heater unit



R. M. HARDGRQVE.

' FLUID HEATER UNIT Jan. 21, 1958 Filed Oct. 20, 1954 2 Sheets-Sheet 1 0 7 a 5 A 5 M f m. m v N4. 2 \1 H i a w. 2 ii M 3 6 w N 4 F m I {A W m 4 n w 5 W w A m 0 a, Q .5 M; N 6 F l 4 .0? 7 m 4 5Q F Ill H P W A. y W... M K. u m. L J

ATTORNEY Jan. 21", 1958 R. M. HARDGROVE FLUID HEATER UNIT Filed Oct. 20, 1954 2 Sheets-Sheet 2 FIG; 4

00000000000000 0OO 'l INVENTOR/ Ralph M. Hardgrpve;

ATTORNEY FLUm HEATER UNIT Ralph Martin Hardgrove, North Canton, @hie, assignor to The Bahcoclr & Wilcox Company, New Yorlr, N. EL, a corporation of New Jersey Application Gctoher 29, 1954, Serial No. 463,388

6 Claims. (Cl. 257-224) The invention herein disclosed relates to an improvement in the construction and operation of a tubular heat exchanger involving particularly the delivery of a gaseous medium thereto. My invention is especially useful in its application to air heater operation wherein the heating medium may be, for example, the hot gaseous products of combustion from a boiler furnace, and the medium to be heated, the major portion of the air required for combustion of fuel within such a furnace.

Y In modern high capacity boiler installations operating, for example, at vapor generating capacities of 500,000 pounds of steam per hour or more, the rate at which heated combustion air must be supplied is often approximately equal to the rate of steam flow. It is also usually required to heat the combustion air to relatively high temperatures, of 500 F. or more, making it necessary to provide an air heater having a considerable area of heat transfer surface to meet the conditions of air flow rate and temperature.

. In a conventional form of air heater wherein the heat transfer elements are in the form of tubes arranged in a bank from one end of the air heater to the other, the air to be heated may be directed over the outer surfaces of the tubes, and a fluid heating medium, such as hot combustion gases, directed through the tubes, the air being suitably directed in series over successive lengths .of tubes in a plurality of cross flow passes in counter flow heat transfer relationship. Where a large capacity cross flow air heater is involved, the inlet for cold air generally extends throughout the full width of the tube bank, which in some instances may involve a cold air inlet of at least 40 feet in Width, the height of the inlet being substantially equal to the height of the first pass across the tubes.

It is known that those portions of the tube lengths in the air inlet pass are subject to fairly rapid corrosion unless the tubes are operated at temperatures high enough to prevent the condensation of'the sulphur trioxide and water vapor in the heating gas passing therethrough. This problem is often met by bypassing a portion of the incoming air around at least a portion of the heat trans fer surface to thereby reduce the cooling effect on the gas discharge end portions of the tubes. However, such bypassing of air reduces the rate of air fiow throughout unit, may result in a decrease in overall efficiency due to the accompany higher gas outlet temperatures.

Condensation of the acid also maintains the heat transfer surfaces in a moist condition, which is conducive to the collection of dust particles on the surfaces and a consequent decrease in heat transfer efficiency. When the heat transfer elements are tubular members and the particle carrying gases are directed therethrougn, such members eventually become plugged and their effectiveness as heat transfer elements is completely nullified.

In a tubular air heater adapted for high capacity operation, it is desirable to have uniform air distribution entering the firstportion of the air heater and throughout the initial air heating stage. In addition, for the reasons previously enumerated, the initial heating must be accomplished in a manner which will not result in condensation of water vapor on the tubes.

Accordingly, an object of this invention is to provide a heat transfer arrangement in air heater in which the first cold air pass is in parallel flow heat transfer relationship with heating gases and succeeding passes are in counter liow heat transfer relationship.

Another object is to provide a fluid heater having an arrangement whereby the fluid to be heated is evenly distributed in efiicient heat transfer relationship throughout the heat exchange passages.

F or an understanding of the invention principles, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawings.

Of the drawings:

Fig. 1 is a vertical sectional view, taken on the line 1-4 of Fig. 2, of an air heater constructed in accordance with the invention;

Fig. 2 is an enlarged partial vertical sectional View taken on the line 22 of Fig. 1;

Fig. 3 is a transverse section taken on the line 33 of Fig. l; and

Fig. 4 is a transverse section taken on the line 4-4 of Fig. l.

The invention is shown as embodied in a tubular type air heater having a high temperature section 10 and a subjacent low temperature section 30. The high temperature section is composed of an inlet chamber 12, having a tube sheet 13, receiving high temperature heating gases from a suitable source, such as a steam genera tor (not shown), and an outlet gas chamber 14-, having a tube sheet 15, with a multiplicity of straight tubes 16 connecting the chambers 12, 14 and providing for heating gas flow therethrough. A casing 18 and transverse baffles 20 are provided external of the tubes 16 and arranged to receive air from a low temperature section 30 and pass the air in successive cross flow passes 22, 24, 26 in counter flow heat transfer relationship. The high temperature heated air leaves by conduit 28 for consequent delivery to the point of use, such as the combustion air supply for the steam generator.

The low temperature section 30 of the air heater is arranged below the high temperature gas outlet chamber 14 and has a gas outlet chamber 32 with a plurality of groups of vertical tubes 34 arranged in transverse rows and connecting said chamber 14 and outlet chamber 32 so as to form a plurality of horizontally spaced heating gas passages. The tubes of each tube group 34 are attached to a tube sheet 36 which forms the base of a corresponding gas passage 38 opening at its top into the outlet chamber 14. The outlet ends of the tubes of all of the tube groups 34 are connected to a common flat tube sheet as.

Low temperature air to be heated is received from a suitable source, such as a forced draft fan (not shown), by an air inlet chamber 41 extending across the entire width of the air heater, and vertically from an elevation above the tube sheet 40 to an elevation subjacent the tube sheet 15. The air then passes from the inletchamber 41 in separate streams into transversely spaced open passes 42 formed by a number of transverse baffles 44 between the tube groups 34. Some of the air also leaves the chamber 41 and flows in open passages 46, said open passages 46 being provided in the shape of an inclined plane block by the baffles 48 which are connected between the tube sheets 36, such passes 46 lie between the gas passages 38. This, there are alternate open passes 46 and heating gas passages 38, including tube groups 34 arranged transversely across the low temperature sec tion of the air heater. The baflies 44 spaced on'either side cfth'e tube groups 34 form restricted longitudinal .fiowtheatitransferflow passages 51 external of the tube groups 34. The air enters said heat transfer passages 51 after having flowed in parallel streams through open passages 42 and 46, Receiving the heated air from the "heat transfer passages 51 is an air outlet chamber 52,.

the air then flowing into a duct 54 to the first pass -22 of the high temperature section of the air heater.

Disposed in each of the'open passages 42, 46 are a number of streamlining baffles 56', 58 which serve the purpose of reducing the turbulence of the incoming air and directing the change in direction of the air in such a manner as to reduce the pressure loss of the entry; Further, these bafiles '56, 58 are arranged to give proper distribution of the incoming air-so as to provide uniform heat transfer conditions in the heat transfer passages.

Thus there is provided an air heater with a low temperature section in which the air flows in longitudinalparallel fiow heat transfer relationship with a low temperature heating gas flowing in tubes and thence into a high temperature section in cross-counter liow heat transfer relationship with the high temperature heating gas in the tubes of the high temperature section of the air heater.

Withthe invention it ispossible to obtain optimum heat transfer from the heatinggases to the combustion air, provide for an elficient increase in air temperature with acorresponding decrease in heating gas temperatures without lowering the tube metal temperatures below that at which. condensation of the heating gas constituents might occur, and provide a means formaintaining a uniform distribution of air throughout. The arrangement of one or more'cross flow heating passes with the substantially parallel flow in the initial heating pass permits a reduction of heating gas temperatures to amounts which will provide for maximum efi'iciency of the power unit generating these gases.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departingfrom such principles;

I claim:

1. A heat exchanger comprising means forming first fluid inlet and outlet chambers, a plurality of heat trans- "fer tubes connecting said chambers for fluid flow therethrough, ,a casing enclosing said tubes to provide a second fluid passageway external of said tubes, and baffle means arranged within said passageway for driecting the second fluid predominantly in a parallel-longitudinal concurrent flow heattransfer relationship with the fiuid in a portion of said tubes and thence in counter and cross flow heat transfer relationship with the fluid in the remaining portion of said tubes.

2. A heat exchanger comprising means forming first fluid inlet and outlet chambers, a plurality of heattransfer tubes connecting said chambers for. fluid flow therethrough, a casing enclosing said tubes to provide a second fluid passageway external-of said tubes, and bafiie means arranged within said passageway .for directing the second fluid predominantly'in a parallel and longitudinal concurrent flow heat transfer relationship with the fluid in a portion of said tubes nearer the first fluid outlet chamber and thence in counter and cross flow heat transfer relationship .with the fluid in the remaining portion of said tubes. a 3. An 'air heater comprising means including groups of tubes forming a plurality of transversely spaced heating gas passages receiving heating gas from a source thereof, ,baflie meansenclosing each of said tube groups and arranged toform alongitudinal flow air heat transfer path throughout the major portion of the length of each of said tube-groups, transversely spaced open passes be- .tweenadjacent tube groups andin communication with the .airin1et-- ends a :of j adjacent. longitudinal flow heat transfer paths containing said tube groups, a

plurality of streamlining vanes disposed Within each *of said open passes, inlet means arranged to provide a flow of air to said open passes, and outlet means arranged to receive said flow of air from said longitudinal flow air heat transfer paths,

4. In an air heater comprising a high temperature section including means forming spaced gas inlet and outlet chambers, heat transfer tubes connecting said chambers, and means for passing air over said tubes in counter 'fiow heat transfer relationship therewith, a low temperature section comprising means including groups of tubes forming a plurality 'of transversely spaced heating gas passages receiving heating gas from said high temperature section gas outlet chamber, baffle 'meansenclosing each of said tube groups and arranged to form a longitudinal flow air heat transfer path throughout the major portion of the length of each of said tube groups, said longitudinal flow air heat transfer paths arranged in parallel, inlet means arranged to provide a flow of air to said longitudinal'flow air heat transfer paths, and outlet means arranged to receive said flow of heated air from said longitudinal flow air heat transfer paths, and means for conducting the heated air from said low temperature section to said high temperature section.

5. In an air heater comprising a high temperature section including means forming spaced gas inlet and outlet chambers, heat transfer tubes connecting said chambers, and means for passing air over said tubes in counter'flow heat transfer relationship therewith, a low temperaturesection comprising meansincluding groups of-tubes forming a plurality of transversely spaced heating gas passages receiving gas from said high temperature section gas outlet chamber, bafiie means enclosing each of said tube groups and arranged to form a longitudinal flow air heat transfer path throughout the major portion of the length of each of said tube groups, transversely spaced open passes between adjacent tube groups and in communication with the air inlet ends of adjacent longitudinal flow heat transfer paths containing said tube groups, said longitudinal flow air heat transfer paths and open passes section comprising means including groups of tubes form- 1 ing a plurality of transversely spaced heating gas passages receiving gas from said high temperature section gas outlet chamber, baffle means enclosing each of said tube groups and arranged to form a longitudinal flow air heat transfer path throughoutthe major portion of the length of each of said tube groups, transversely spaced open'passes between adjacent tube groups and in communication with the air inlet ends of adjacent longitudinal flow heat transfer paths containing said tube groups, a plurality of streamlining vanes disposed Within each of said open passes, inlet means arranged to provide a flow of air to said open passes, and outlet means arranged to receive said flow of air from said longitudinal flow air heat transfer paths, and means for conducting the heated airfrom said low temperature section said high temperature section.

References Cited in the file of this patent UNITED STATES PATENTS Berkeley etal Nov. 26, 1940 Marshall June 13,1950 Worn a Sept, 19, 0 

